Articulation points

/* */

#include <vector>
#include <iostream>
#include <set>

using namespace std;

class Graph {
public:
    explicit Graph(size_t v_amount) : graph(v_amount + 1), visited(v_amount + 1), tin(v_amount+1, v_amount+1),
    up(v_amount+1, v_amount+1), from(v_amount + 1), children(v_amount+1){
    }

    void add_e(size_t a, size_t b) {
        graph[a].push_back(b);
        graph[b].push_back(a);
    }

    vector<size_t> get_articulation_points(){
        time = 0;
        for(size_t v = 1; v < graph.size(); ++v){
            if (visited[v] == 0){
                dfs(v);
                if (children[v] < 2){
                    art_points.erase(v);
                }
            }
        }
        art_points.erase(0);
        return {art_points.begin(), art_points.end()};
    }


    void dfs(size_t v){
        visited[v] = 1;
        ++time;
        tin[v] = time;
        for (auto neighbour : graph[v]){
            if (visited[neighbour] == 0){
                from[neighbour] = v;
                children[v]++;
                dfs(neighbour);
                up[v] = min(up[v], up[neighbour]);
                if (up[neighbour] >= tin[v]){
                    art_points.insert(v);
                }
            }
            if (visited[neighbour] == 1 && from[v] != neighbour){
                up[v] = min(up[v], tin[neighbour]);
            }
        }
        visited[v] = 2;
    }

    vector<size_t> children;
    vector<size_t> from;
    set<size_t> art_points;
    size_t time;
    vector<size_t> tin;
    vector<size_t> up;
    vector<int> visited;
    vector<vector<size_t>> graph;
};


int main(){
    size_t v_amount, e_amount;
    cin >> v_amount >> e_amount;
    Graph graph(v_amount);
    for (int i = 0; i < e_amount; ++i){
        size_t a, b;
        cin >> a >> b;
        graph.add_e(a, b);
    }
    auto ap = graph.get_articulation_points();
    cout << ap.size() << endl;
    for (auto v : ap){
        cout << v << endl;
    }
    return 0;
}